Refrigeration system with defrosting means



June 12, 1962 H. F. V. BODCHER 3,038,317

I REFRIGERATION SYSTEM WITH DEFROSTING MEANS Filed Aug. 25, 1958 Hlllll llllllll INVENTOR Herman FredrLK VL'lheLm Bliclcl'ner ATTORNEYS Unite tats Patent 3,038,317 Patented June 12, 1962 3,038,317 REFRIGERATION SYSTEM WITH DEFROSTING MEANS Herman Fredrik Viihelne Biidcher, Molinvagen 4, Bronnna, Sweden Filed Aug. 25, 1958, Ser. No. 756,935 Claims priority, appiication Sweden Aug. 29, 1957 4 Ciairns. (Cl. 62-151) This invention relates to a refrigeration system of the type comprising a compressor, a condenser for the compressed refrigerant, a container for liquid refrigerant, and an evaporator. In conventional systems of this type, a flow restriction member is inserted between the container and the evaporator. Due to the reduction of the pressure during the flow of the liquid refrigerant through the restriction member, part of the liquid is evaporated, and its temperature is decreased. Such evaporation causes certain losses, since a smaller amount of liquid refrigerant is accessible to absorb heat in the evaporator. Said losses are likely to amount to about 20 percent or even more.

In the conventional systems control is effected in response to variations in the pressure or temperature at the low pressure side of the system by means of an automatically or thermostatically operating expansion valve, or the supply of refrigerant to the evaporator is made responsive to the pressure difference between the high pressure side and the low pressure side, in which case capillary tubes may serve as flow restriction members.

Conventional refrigeration systems suffer from the inconvenience that ice deposited on the evaporator must be removed mechanically, which is difficult and time-wasting, or by heating which may result in an undesired heating of the space surrounding the evaporator and also results in a reduction of the average output of the system.

The present invention relates to a refrigeration system substantially of the type referred to, but in which the above inconvenience resulting from the formation of ice is avoided. The system according to the invention is substantially characterized by the fact that between the liquid container and the evaporator there is provided a valve adapted to be opened when the pressure in the container exceeds a predetermined value and to be closed again When the pressure in the container falls below a predetermined lower value. Consequently, refrigerant will be supplied to the evaporator intermittently and substantially Without restriction, resulting in an elimination of the above named losses due to adiabatic expansion. Instead thereof, the heat contents of the liquid refrigerant is used to melt the ice which is formed on the outside of the evaporator in the intervals between two opening periods of the valve. Instead of spending extra caloric energy for melting the ice, the amount of heat consumed in melting the ice is used, in accordance with the invention, to decrease the temperature of the liquid refrigerant, whereas in conventional systems said decrease in temperature takes place at the adiabatic change of state in the restriction member.

The invention is described more closely hereinbelow with reference to embodiments thereof illustrated in the accompanying drawings:

FIG. 1 is a diagrammatic view of a refrigeration system according to the invention;

FIG. 2 illustrates a practical construction of an evaporator for a system according to the invention;

FIG. 3 is a diagrammatic view of an evaporator arranged, for instance, in connection with a cooled store counter; and

FIG. 4 illustrates a modified embodiment of the system according to FIG. 1.

The system shown in FIG. 1 operates with a suitable conventional refrigerant, such as Freon. The gaseous refrigerant is compressed in a compressor 1 which delivers the refrigerant to a condenser 2 which may be air-cooled. In the condenser 2, the refrigerant is condensed Whereupon it flows down into a container 3.

From the lower part of the container 3' a tube 4 including a valve 5 extends upwards. The tube 4 merges into a diagrammatically illustrated evaporator 5 which communicates with the upper part of a collecting vessel 7. A return tube 8 connects the bottom of the collecting vessel 7 with the tube 4- at a place between the valve 5 and the evaporator 6. The return tube 8 comprises a non-return valve 9 which prevents flow of refrigerant from the tube 4 to the collecting vessel 7 and permits flow in the opposite direction.

A conduit 10 connected to the upper part of the collecting vessel 7 returns evaporated refrigerant to the suction side of the compressor 1.

The valve 5 is a so-called two-pressure valve adapted to be opened when the pressure in the container 3 exceeds a predetermined value and to be closed again when the pressure in the container falls below a predetermined lower value. The pressure control line from the container to valve 5 is shown at 4.

The mode of operation of the system is as follows:

When the valve 5 is closed, the container 3 will be successively filled with liquid flowing down from the condenser 2. The liquid rises eventually into the condenser 2 which is at a higher level than the container 3, and the condenser will be successively filled with liquid. As a result thereof, the cooling surface of the condenser exposed to the gaseous refrigerant will be decreased, and condensation of the gaseous refrigerant will thus take place at a lower rate, resulting in an increase of pressure in the condenser and in the container 3.

When the pressure in the container 3 attains a predetermined maximum value, the valve 5 will be fully opened, and liquid refrigerant will rapidly flow upwards through the tube 4 and the evaporator 6. Since the liquid refrigerant can be assumed to be at substantially room temperature, the ice coating on the evaporator 6 will be melted and, at the same time, the temperature of the liquid refrigerant will be decreased. Liquid refrigerant also flows up into the collecting vessel 7'. After a very short time, the pressure in the container 3 has fallen to a predetermined minimum value causing the valve 5 to close again. The compressor 1 operates continuously and withdraws evaporated refrigerant from the vessel 7 through the conduit 10, and the compressed refrigerant will be again normally condensed in the condenser 2. Evaporation in the evaporator 6 also takes place in the normal manner. If the liquid level in the evaporator 6 tends to be lowered, replenishment takes place at the lower end of the evaporator from the return tube 8 to keep the evaporator always filled with liquid refrigerant.

The container 3 and the vessel 7 are so dimensioned relative each other that the condenser 2 will begin to be filled with liquid before the vessel 7 is entirely emptied. Further, the maximum pressure in the container 3 has a value such that the valve 5 will be opened substantially at the time when the vessel 7 is about to be entirely emptied, resulting in that the evaporator 6 will always be filled with liquid refrigerant. By dimensioning the container 3 and the vessel 7 with consideration to the capacity of the compressor it is possible to determine the intervals between two consecutive opening periods of the valve 5, which periods should be chosen such that the ice-coating on the evaporator will be completely melted If the system is properly dimensioned, the surface of the evaporator will practically always be free from ice, resulting in a very favourable transfer of heat from the ambient atmosphere to the evaporator. Since there are no flow restriction members in the system other than valve which, however, is ,either fully open or completely closed and does not oifer any appreciable resistance to flow of the liquid refrigerant when in an open position, the system is practically insusceptible to the worts enemies of a conventional refrigeration system, namely, moisture, dirt and air. The defrosting periods are comparatively short and amount to, for instance, 30 to 60 seconds. Due to the high velocity of the refrigerant in the evaporator, return of oil to the compressor is ensured, and the inner surfaces of the evaporator are always kept free from oil, resulting in a high transfer of heat.

FIGS. 2 and 3 illustrate two practical arrangements of an evaporator in a compartment such as, for example, a cooling-room. According to FIG. 2, the evaporator 6 consists of a plane coil having vertical turns located right above the upwardly inclined supply tube 4 for the liquid refrigerant. When the ice layer is melted, the water will flow down along the turns of the coil and be caught by the slanting supply tube 4 along which the water flows out of the cooling-room to be collected, for instance below a manifold which is indicated at 11 in FIG. 2 and is common to a plurality of evaporators 6.

According to FIG. 3, an evaporator 6 in a coolingroom is housed within a perforated screen 12 which may be close to the evaporator, since no thick ice layers will be deposited thereon. The screen 12 prevents direct contact between articles in the cooling room and the evaporator 6 and thereby prevents articles from getting frozen to the evaporator.

In the embodiment according to FIG. 4 the tube 4 is connected to the evaporator 6 at a point between the ends of the latter which ends are connected to the vessel 7. The lower portion of the evaporator offers a certain resistance against the fiow of refrigerant so that there is no need for a non-return valve.

The valve 5 is by-passed by a conduit 13 of relatively small cross-sectional area through which there is a continuous flow of refrigerant. The capacity of this by-pass conduit is smaller than that of the compressor 1. By this arrangement the intervals between the opening periods of valve 5 are extended as it will take a longer time for the compressor .1 to raise the pressure in the container 3 on amount of the continuous bleeding through conduit 13. Naturally this narrow conduit may be replaced by a wider conduit having a restriction member.

The condenser 2 is by-passed by a conduit 14. Normally the refrigerant passes through the condenser but after the valve 5 is opened and the liquid refrigerant is blown out of the container 3 gaseous refrigerant of a relatively high temperature passes upwards through the evaporator 6 for a time sufiicient for the melting of the ice coating. The closing of the valve 5 may be delayed to allow the water to drip off from the evaporator. This arrangement is preferable in systems where the ice-formation is heavy.

The invention is not limited to the above described and illustrated embodiments which may be modified within the scope of the appending claims. It is important that the condenser 2 be so located relative to the container 3 that it will begin to be filled as soon as the liquid in the container 3 reaches a certain level or becomes entirely filled. The collecting vessel 7 need not be located above the evaporator, but should be placed and arranged such as to ensure the return of liquid refrigerant through the return tube 8 to the lower end of the evaporator 6. The valve 5 is controlled in response to pressure conditions on the high pressure side, but since increased pressure results in an increase of temperature in the condenser 2, the valve 5 may be controlled in response to the temperature prevailing in the condenser. Also pure time control is possible. Other modifications are conceivable and need not be mentioned here.

What I claim is:

1. In a refrigeration system, the combination comprising a compressor, a condenser having its inlet connected to the outlet from said compressor, a container for liquid refrigerant connected to the outlet from said condenser, an evaporator, a first conduit leading to the inlet to said evaporator from the outlet from said container, a coliecting vessel located above said evaporator, a second conduit connecting the outlet from said evaporator to said collecting vessel, the outlet end of said second conduit opening into said collecting vessel at a distance above the bottom of the latter, a third conduit leading from the outlet from said collecting vessel to the inlet to said compressor, a pressure responsive valve device disposed in said first conduit, said valve device being adapted to fully open said first conduit when the pressure in said container exceeds a predetermined value and to fully close said first conduit when the pressure in said container falls below a predetermined lower value, thereby to effect a supply of liquid refrigerant to said evaporator in an intermittent manner and substantially without restriction in accordance with the corresponding intermittent decreases and increases in pressure in said liquid refrigerant in that part of the system between said valve and the compressor outlet.

2. A refrigeration system as defined in claim 1 wherein the inlet to said evaporator from said first conduit is located intermediate the ends of said evaporator and wherein both ends of said evaporator are connected to said collecting vessel.

3. In a refrigeration system of the evaporative type, the combination comprising a compressor, a condenser having its inlet connected to the outlet from said compressor, a container for liquid refrigerant connected to the outlet from said condenser, an evaporator, a conduit leading to the inlet to said evaporator from the outlet from said container, conduit means for returning refrigerant from the outlet from said evaporator to the inlet to said compressor, a valve device responsive to the pressure in said container and disposed in said conduit leading to the inlet to said evaporator, said valve device being adapted to fully open said last-named conduit when the pressure in said container exceeds a predetermined value and to fully close the conduit when the pressure in said container falls below a predetermined lower value, thereby to effect a supply of liquid refrigerant to said evaporator in an intermittent manner and substantially without restriction in accordance with the corresponding intermittent decreases and increases in pressure in said liquid refrigerant in that part of the system between said valve and the compressor outlet, and a restricted conduit by-passing said valve device, said restricted conduit serving to continuously bleed a small amount of liquid refrigerant from said container and thereby extend the intervals between successive openings of said valve device.

4. In a refrigeration system of the evaporative type, the combination comprising a compressor, a condenser having its inlet connected to the outlet from said compressor, a container for liquid refrigerant connected to the outlet from said condenser, an evaporator, a conduit leading to the inlet to said evaporator from the outlet from said container, conduit means for returning refrigerant from the outlet from said evaporator to the inlet to said compressor, a valve device responsive to the pressure in said container and disposed in said conduit leading to the inlet to said evaporator, said valve device being adapted to fully open said last-named conduit when the pressure in said container exceeds a predetermined value and to fully close the conduit when the pressure in said container falls below a predetermined lower value,

thereby to effect a supply of liquid refrigerant to said whereby refrigerant may flow directly from the outlet evaporator in an intermittent manner and substantially from Said compressor to the inlet to Said container- Without restriction in accordance with the corresponding References Cited in the file of this patent intermittent decreases and increases in pressure in said UNITED STATES PATENTS liquid refrigerant in that part of the system between said 5 1 874 294 Nesbitt AuCr 30 1932 valve and the compressor outlet, and a conduit by-pass- :9 5: Youst z: 1934 ing said condenser between the inlet and outlet thereof 2,667,757 Shoemaker Feb. 2, 1954 

